Prosecutor Chris Owens began his opening statement by playing an audio recording of the confrontation and pointed out one voice barking commands: "Don't let nobody outta here ... stand the (expletive) up before it gets ugly in here."
Simpson, who flashed a thumbs-up sign when he arrived at court, sat impassively while Owens described the rest of the recording.
"The audio will show threats, it will show force, it will show demands and it will show the taking of property from the victims in this case," Owens said.
"In our presentation of the evidence we are going to spend the next few days finding which may be the true face of ... Simpson, not necessarily the one he tries to put out to the world," Owens said.
In the defense opening, Simpson's attorneys were expected to tell the jury that when he and five other men pushed into the hotel room to confront the memorabilia peddlers, they were trying to retrieve family heirlooms Simpson hoped to pass on to his children.
"My client was recovering personal property that was stolen from his home many years prior," Simpson lawyer Yale Galanter said Friday. "This is not a case about sports memorabilia. It's about personal property."
Simpson, 61, and co-defendant Clarence "C.J." Stewart, 54, a former golfing buddy from North Las Vegas, have pleaded not guilty to 12 charges including kidnapping, armed robbery and conspiracy. Each could face life in prison with the possibility of parole if convicted of kidnapping, and mandatory prison time if convicted of armed robbery.
Clark County District Attorney David Roger has said the case against the two men will rely on testimony from some 25 witnesses, including four former co-defendants who have taken plea deals and agreed to testify for the prosecution.
After opening statements, the prosecution is expected to call Bruce Fromong, a 54-year-old sports collectibles dealer from North Las Vegas to the stand, according to a witness list that Galanter said prosecutors shared with the defense.
Fromong testified at a hearing in November that he expected to meet with an anonymous buyer when Simpson arrived with others "in a military invasion fashion."
Fromong said one man wielded a gun while Simpson shouted that items in the room belonged to him and instructed the men with him to gather them up.
Simpson denies that guns were taken to the hotel room.
The prosecution audio recordings were surreptitiously made by Thomas Riccio, a Los Angeles collectibles trader who arranged the Sept. 13, 2007, meeting between Simpson, Fromong and sports memorabilia dealer Alfred Beardsley.
Galanter said the recordings could also help the defense.
"It'll be clear from the tapes when O.J. says 'Don't take any things that aren't mine,'" Galanter said.
By Associated Press Writer Ken Ritter; AP Special Correspondent Linda Deutsch contributed to this report